Atherosclerotic arterial disease is the leading cause of morbidity and mortality in the United States and most other developed countries. Atherosclerosis is a chronic disease process characterized by lipid deposits and fibrosis of the intima, irregularly distributed in large and medium sized arteries. The disease is progressive and most often becomes clinically manifest in the middle-aged and elderly. When severe, the atheroschlerotic plaque causes a reduction of the cross-sectional area of the arterial lumen, with and without thrombosis. Resultant ischemic manifestations include: angina pectoris, myocardial infarction, stroke, intermittent claudication, gangrene of the lower extremities and renovascular hypertension.
The current management of atherosclerotic disease includes preventative therapy aimed at minimizing known major risk factors such as hypertension, smoking, hypercholesterolemia and diabetes mellitus.
Coronary artery bypass grafting (CABG), carotid endarterectomy and bypass grafting (autogenous vein or synthetic graft) of the iliac, femoral and renal arteries are all well established surgical methods of palliative therapy. Although these procedures are often effective in relieving ischemia, each of these represents a major surgical operation with significant associated morbidity, mortality and expense. CABG, for example, requires the opening of the chest cavity (thoracotomy) and use of cardiopulmonary bypass, with not uncommon postoperative complications including postpericardotomy syndrome, Non-A Non-B hepatitis, stroke and a mortality of approximately one percent (1%) at most medical centers.
Percutaneous transluminal angioplasty (PTA) by means of a balloon catheter is a relatively new ("non-surgical") procedure with proven efficacy in relief of atheroschlerotic obstruction of the coronary, renal and peripheral circulations. The technique involves the percutaneous passage (under local anesthesia) of a specialized balloon-tipped catheter through the site of arterial narrowing, and inflation of the balloon to reduce obstruction. This is always done in conjunction with angiographic visualization of the vessel being treated. When successful, this procedure results in a reduction of the arterial stenosis and a decrease in the transstenotic pressure gradient. The mechanism of action is felt to consist of some combination of plaque compression, intimal splitting and medial/adventitial stretching. Healing of the balloon-damaged plaque may involve fibrosis and retraction of the split intimal elements, with further luminal enlargement in the weeks to months following the procedure.
The safety and efficacy of PTA is a function of the vessel being treated, patient selection, and the expertise of the physician performing the procedure. Primary angiographic success, defined as 20% or greater reduction of stenosis, is now achieved in approximately 80-90% of attempts in carefully selected patients at experienced centers. The obvious advantage of PTA, compared to surgical palliative therapy, is that it does not require major surgery or general anesthesia with the associated sequelae.
Despite its proven efficacy in the palliation of obstructive atherosclerotic disease, PTA, as it is currently performed, has several important technical limitations. These limitations are particularly true in the application of PTA to the coronary circulation.
Even in the most skilled hands, dilation of an arterial obstruction is currently not achievable in approximately 20% of attempts. The most common cause of failed PTA is the inability to pass either the guide wire or dilating catheter through the site of a tight or eccentric stenosis. This problem is even more common in attempts to dilate the difficult to access right and circumflex coronary arteries. Although technical advances, such as steerable catheters, have reduced the frequency of unsuccessful attempts, inability to cross a tight, eccentric or fully closed stenosis remains a major limitation of PTA.
Attempts at balloon or guide wire passage in vessels which are tightly stenotic may lead to arterial dissection and/or acute occlusion necessitating emergency vascular surgery. This major complication occurs in 6-8% of attempts at coronary angioplasty.
Inability to dilate an obstruction, even after proper balloon positioning and inflation is a second common mode of PTA failure. This problem is most frequently encountered in older plaques which are densely fibrotic and/or calcified.
Restenosis of the obstructed arterial segment following successful PTA is a major problem with the current technique. This problem is more common following PTA of a coronary obstruction (30-35% at one year) than in the peripheral circulation (10-15% at two years). Pharmacologic attempts to reduce the incidence of restenosis have been largely unsuccessful.
Distal embolization of atherosclerotic plaque following balloon PTA occurs in approximately 5% of patients undergoing PTA of lower extremity or renal arteries. Although these emboli are usually clinically insignificant in these vascular territories, such embolization could be catastrophic in the cerebral circulation. For this reason, balloon PTA is considered to be contraindicated for the treatment of obstructive lesions in the arteries of the aortic arch, such as the carotid artery.
In U.S. Pat. No. 4,207,874 (dated June 17, 1980) D. S. J. Choy describes a means for using a laser beam to tunnel through an arterial occlusion by vaporization of the obstruction. The difficulty with Choy's invention is that that there is insufficient means to prevent simultaneous destruction of the arterial wall. For example, the Choy invention shows an intense laser beam directed in the forward direction without significant beam attenuation in that direction. If the artery were to curve and the arterial wall was exposed to the laser beam, the wall could also be vaporized which could be catastrophic for the patient. Although the Choy invention describes a means for direct visualization of the obstructed region, it does not describe a centering means or a guide wire following means in order to guarantee that the laser beam does not illuminate part of the arterial wall. Furthermore, the Choy invention may completely obstruct a partially obstructed artery thereby cutting off blood flow to distal tissues for a significant time period. The result is ischemia which could cause irreparable damage to heart or brain tissue. Furthermore, if laser oblation was used in the carotid arteries, the resulting gas bubble formation would undoubtedly cause some cerebral ischemia resulting in permanent brain damage.
In U.S. Pat. No. 4,273,128 (date June 16, 1981) B. G. Lary describes a "Coronary Cutting and Dilating Instrument" used for opening a coronary stenosis that is restricting blood flow. The device described by Lary could not be used in a completely or nearly completely occluded artery because its "blunt ovoid tip" could not pass through a completely occluded vessel. Furthermore, the Lary invention does not have any means to prevent its cutting blade from cutting through the arterial wall as well as occluding the stenotic material. Furthermore, there is no means taught in the Lary patent for centering the cutting blade within the arterial walls. Thus, if the probe wire 13 (of FIG. 10) of the Lary invention guides the knife through a highly eccentric lumen within the stenotic plaque its knife blade would surely cut through the arterial wall which would have serious adverse effects for the patient.
In a prior patient application Ser. No. 874,140 filed on June 13, 1986, by Robert E. and Tim A. Fischell which is entitled "A Guide Wire Following Tunnelling Catheter System for Transluminal Arterial Angioplasty" there is described a means for removing stenotic plaque by advancing a tunneling catheter through a guiding catheter and around a guide wire. In that prior invention, the cutting is done by advancing the cutting catheter in a forward (anterograde) direction. A potential difficulty in such a procedure is the inability to exert enough forward force to cut through a hard calcified plaque. Furthermore, if the tunneling catheter is advanced too far in the forward direction, it could cut the arterial wall. Even with the use of cutting (as opposed to fracturing the plaque which occurs with balloon dilation) there would still be the possibility of some particulate matter flowing into the bloodstream which could result in some distal ischemia.
It is the goal of the present invention to eliminate the numerous shortcomings of the prior art in order to provide a device which can safely tunnel a clean hole through virtually any arterial stenosis without the possibility of cutting the arterial wall or creating gas bubbles, or causing the release of particulate matter into the bloodstream.